© Koninklijke Philips Electronics N.V. 2005. All rights reserved.
User manual
Rev. 03 — 7 June 2005
100 of 139
Philips Semiconductors
UM10119
P89LPC938 User manual
13.7 SPI clock prescaler select
The SPI clock prescalar selection uses the SPR1-SPR0 bits in the SPCTL register (see
14. Analog comparators
Two analog comparators are provided on the P89LPC938. Input and output options allow
use of the comparators in a number of different configurations. Comparator operation is
such that the output is a logic 1 (which may be read in a register and/or routed to a pin)
when the positive input (one of two selectable pins) is greater than the negative input
(selectable from a pin or an internal reference voltage). Otherwise the output is a zero.
Each comparator may be configured to cause an interrupt when the output value changes.
14.1 Comparator configuration
Each comparator has a control register, CMP1 for comparator 1 and CMP2 for comparator
2. The control registers are identical and are shown in
The overall connections to both comparators are shown in
. There are eight
possible configurations for each comparator, as determined by the control bits in the
corresponding CMPn register: CPn, CNn, and OEn. These configurations are shown in
.
(1) Not defined
Fig 45. SPI master transfer format with CPHA = 1.
1
2
3
4
5
6
7
8
MSB
LSB
6
1
5
2
4
3
3
4
2
5
1
6
LSB
MSB
MSB
LSB
DORD = 0
DORD = 1
6
1
5
2
4
3
3
4
2
5
1
6
LSB
MSB
002aaa937
Clock cycle
SPICLK (CPOL = 0)
SPICLK (CPOL = 1)
MOSI (input)
MISO (output)
SS (if SSIG bit = 0)
DORD = 0
DORD = 1
